This invention relates to etching magnetic materials, and particularly to etching iron-silicon-aluminum trialloys.
Magnetic materials are employed in a variety of applications, particularly in the electronic arts. It is common, for example, to employ thin films of magnetic materials in magnetic transducers for reading and writing digital data on media, the patterns of the thin films being at least partially defined through etching processes. For example, magnetic nickel-iron alloys such as Permalloy are commonly etched with ferric chloride (FeCl.sub.3); magnetic crystals of manganese-zinc-ferrite are etched with phosphoric acid (H.sub.3 PO.sub.4). However, no chemical etchant is known for selected etching of iron-silicon-aluminum trialloys.
Sendust is a particularly useful magnetic iron-silicon-aluminum trialloy used in the electronic arts containing about 83 weight percent iron or more and exhibiting a higher saturation magnetization than ferrite. Typical compositions of Sendust contain between about 83 wt % and 94 wt % iron, 4 wt % and 11 wt % silicon and 2 wt % and 6 wt % aluminum. However, there is no known chemical etchant useful for selectively etching patterns in thin films of iron-silicon-aluminum alloys. Consequently, when employing such alloys in electronic devices, such as in magnetic heads, it has been necessary to carefully control the deposition of the of the magnetic alloy through masks and the like. If etching was required, it had to be accomplished through a physical etch, such as an ion milling or sputter etch.
Nitric acid is a well-known etchant for iron. It is theorized that iron-silicon-aluminum alloys have not been successfully chemically etched with nitric acid prior to the present invention because nitric acid causes oxides of silicon and aluminum to thicken and adhere better over the ferrite-silicon-aluminum alloy, thereby inhibiting further etching of the alloy.